Aircraft are often equipped with a Traffic Advisory Systems (TAS) or Traffic Alert and Collision Avoidance System (TCAS) to provide traffic awareness functionality. TAS/TCAS systems are designed to interrogate target aircraft transponders and receive their replies, then process these replies to generate range and bearing to the target aircraft.
For example, TAS/TCAS systems transmit interrogation signals that are received and responded to by other aircraft and used to determine the location of the other aircraft relative to the interrogating aircraft's position. TAS/TCAS typically includes a four-element passive phased-array antenna electrically connected by coaxial cables to a radio-frequency transceiver. During transmission operations the antenna performs antenna pattern formation, and during reception operations the antenna determines bearing angles to the other aircraft. The transceiver is electrically connected to a signal processor that controls transmission and reception of TAS/TCAS-related information and performs aircraft surveillance operations such as traffic alert and collision avoidance operations.
TAS/TCAS identifies the locations and tracks the movements of other aircraft that are equipped with transponders, including determining ranges and bearings to the other aircraft based on response signals received from the other aircrafts' transponders. More specifically, the responses from interrogated aircraft include information that allows them to be located in cylindrical coordinates relative to the interrogating aircraft. This information is processed to estimate when the other aircraft may enter into the proximity of the interrogating aircraft and when the user should be made aware of the other aircraft with traffic advisories and resolution advisories (RAs) to move away from the other aircraft.